The invention relates to boron containing ceramic-aluminum metal composites. In particular, the invention relates to boron carbide-aluminum composites.
Aluminum-boron carbide (ABC) composites are of interest for components, such as computer hard drive disks, because of their lower density and higher stiffness than aluminum metal. One of the most desirable methods of forming complex shapes of aluminum-boron carbide composites has been to infiltrate a boron carbide preform with aluminum. The infiltration method results in a dense ABC composite having essentially the same geometry and dimensions as the porous preform.
Unfortunately, because aluminum metal has an aluminum oxide layer, infiltration has to be performed at a high temperature (i.e., above 1000xc2x0 C.). Thus, infiltration has required the use of preforms that are self-supporting. This has precluded the use of substantial amounts of aluminum in the preform. This is because the preform slumps and incompletely infiltrates due to melting of the aluminum in the preform and sintering and reacting with the boron carbide causing the pores to be closed off from the infiltrating metal. Consequently, infiltrated ABC composites have been limited to high boron carbide concentrations (i.e., at least about 40 percent by volume). The lower limit for a self-supporting porous particulate body is generally considered to be 40 percent particulates and the balance pores.
Other techniques have been used to form ABC composites with high aluminum concentrations, such as solid state sintering and high pressure techniques below the melting temperature of aluminum. However, sintering at temperatures below the melting temperature of aluminum suffers from sintering shrinkages resulting in costly machining and, consequently, only making simple shapes economically viable. Similarly, high pressure techniques, such as extruding aluminum and boron carbide, are expensive and limited in the shapes that can be made. In addition, since the aluminum does not melt in these techniques, the bonding between the boron carbide is substantially less compared to when the aluminum melts and reacts with the boron carbide. Consequently, a composite with less than optimal properties is formed by these techniques.
In addition, boron carbide has been cast in molten aluminum, but since boron carbide reacts quickly with molten aluminum and decomposes into boron metal, carbon and water soluble aluminum carbide, the boron carbide is first encapsulated with a protective metal, such as silver. These techniques suffer from the inability to control detrimental phases that reduce strength (e.g., Al4C3) in the absence of an additional expensive step of coating the boron carbide prior to casting. This protective layer precludes the boron carbide to interfacially bond (react) with the aluminum to make, for example, a stronger composite.
Accordingly, it would be desirable to provide a material and method that overcomes one or more of the problems of the prior art, such as one of those described above.
A first aspect of the invention is a method of forming a boron containing ceramic-aluminum metal composite comprising,
(a) mixing a boron containing ceramic with a metal powder comprised of aluminum or an aluminum alloy, where the boron containing ceramic is reactive with aluminum above the melting temperature of aluminum,
(b) shaping the mix of step (a) into a porous preform,
(c) contacting the porous preform with an infiltrating metal comprised of aluminum or aluminum alloy having a lower melting temperature than the metal powder, and
(d) heating the porous preform and infiltrating metal to an infiltrating temperature sufficient to melt the infiltrating metal but insufficient to melt the metal powder, such that the infiltrating metal infiltrates the porous preform and forms a substantially dense boron containing ceramic-aluminum metal composite.
Surprisingly, the method is capable of producing, for example, a substantially dense near net shape boron carbide-aluminum metal composite below the melting temperature of pure aluminum (i.e., 660xc2x0 C.) using infiltration. xe2x80x9cSubstantially densexe2x80x9d means a body that is at least 95 percent of theoretical density. In addition, the method allows improved bonding between, for example, boron carbide and aluminum due to the production of reaction phases between the boron carbide and aluminum in a controlled manner due to the low infiltration temperatures. This in turn allows the production of a novel boron carbide-aluminum body having a high concentration of aluminum that has improved bonding due to the controlled reaction of the lower melting temperature aluminum with boron carbide.
A second aspect of the present invention is a boron containing ceramic-aluminum metal composite having a density of at least about 95 percent of theoretical density and being comprised of at least about 60 percent by volume aluminum metal or alloy thereof, with the boron containing ceramic and at least one reaction product of the boron containing ceramic and aluminum dispersed within the aluminum metal or alloy thereof.
A third aspect of the present invention is a boron containing ceramic-aluminum metal composite having a density of at least about 95 percent of theoretical density and being comprised of at least about 30 percent by volume aluminum metal or alloy thereof, with the boron containing ceramic and at least one reaction product of the boron containing ceramic and aluminum dispersed within the aluminum metal or alloy thereof, with the proviso that at most a trace of Al4C3 is present in the composite.
The ceramic-metal composite may be used in applications benefiting from properties, such as low density and higher stiffness than aluminum metal. Examples of components include hard drive components (e.g., E-blocks, suspension arms, disks, bearings, actuators, clamps, spindles, base plates and housing covers); brake components (e.g., brake pads, drums, rotors, housings and pistons); aerospace components (e.g., satellite mirrors, housings, control rods, propellers and fan blades); piston engine components (e.g., valves, exhaust and intake manifolds, cam followers, valve springs, fuel injection nozzles, pistons, cam shafts and cylinder liners) and other structural or recreational components (e.g., bicycle frames, robot arms, deep sea buoys, baseball bats, golf clubs, tennis rackets and arrows).